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Lecture

EESA09H3 Lecture Notes - Migraine, Heptachlor, Hydrostatic Equilibrium


Department
Environmental Science
Course Code
EESA09H3
Professor
Tanzina Mohsin

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Lecture 7
Land/Sea Breeze
-Thermally induced circulation
- Causes pressure differences
- Often associated with day and night contrasts (diurnal variation)
-Land/sea breezes arise from differential heating of the earth‟s surface on a daily (diurnal) basis. Land surfaces
heats more rapidly and cools more rapidly than water surfaces. During the day, the land surface is typically
warmer than the water surface. Warmer air rises and so air is rising over the land and sinking over the water. To
complete the circulation air moves from the water area to the land area at the surface. This forms a cool breeze
at the surface and is called a sea or lake breeze. It is particularly noticeable during the day in the summer. At the
upper level there is a reverse flow with air moving out over the water. At night the opposite occurs, the water
surface is warmer than the land. Air rises over the water and sinks over the land. The induced surface flow is
from land to water or a land breeze. Sea breezes are strongest in the summer when the temperature contrast is
the greatest. Even on seasonal scales, bodies of water warm up and cool down slower than land masses. In the
summer, therefore, the average temperature of the land over the entire 24 hour period is warmer than the
average sea temperature; the diurnal heating of the land mass adds to this seasonal difference to create a larger
temperature contrast. Land breezes, for similar reasons, are stronger in the winter.
Monsoon
-Arabic word mausim meaning season. Referred to seasonal trade winds in Arabian sea
-Seasonal scale thermal wind
-Asian Monsoon
- Large scale impacts on India and surrounding countries (South Asia) and Africa
-Summer monsoon begins late may
-During the winter months, the Indian Ocean is warmer than the surrounding land mass and air rises over the
ocean and sinks over the land inducing a land breeze and dry conditions. During the summer, the land is warmer
than the Indian Ocean. Air rises over land and sinks over the water. This induces a sea breeze. This breeze has
high moisture content. As the air moves over the land, it rises, cools and water vapour condenses into water
droplets (clouds) generating copious amounts of rain. The monsoon persists into the fall.
Valley Breeze
-Smaller scale wind
-Also driven by diurnal variations in heating
-During the day, land warms faster than the air and upslope winds are induced
-At night, the opposite occurs and downslope winds are induced
-Important features for hikers
Katabatic Wind
-Another mountain wind
-Air passing over a glacier or ice sheet becomes very cold and dense
-Cold air funnels into valleys producing cold strong winds
Chinook
-Winds on the lee side of mountains foehn wind
-It is a North American term
-Linked to migraine headache occurrence
Urban Heat Island
-the warming of the urban areas and the surrounding areas
-most noticeable at night and in the winter months
-more intense when winds are non-existent

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Four factors contributing
1. Reduced evaporation
Buildings, pavement prevent evaporation
Lack of vegetation which would bring water up from the soil
More energy goes into heating the surface and less into evaporation this enhancing the heating
2. Reduced Albedo
During winter months, snow is removed which decreases albedo from urban areas and thus more
energy is absorbed
3. Heat Storage
Tall buildings create a complex geometry canyon effect
Radiant energy is trapped by buildings
Wind is blocked, preventing convective cooling
4. Heat Generation
Industry, motor vehicles, domestic heating and air conditioning release large quantities of heat
Some types of urban pollution prevent release of excess heat
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